Potentiometer



Oct. 20, 1959 A. L oNG l 2,909,747

POTENTIOMETER Filed July 2, 1958 2 Sheets-Sheet l ve--`;" "z T-e k|o-|Aa/e k1' @3.7L 1L i FIG. l l; :v 3 IJ 3 E |56 l l "8 l 52 i I 86 Q A 72el G, I I lj/ /ez 26 l l 24 e 541 .esel E 44 24 .85e 58 l 84 g ,85e|v EE I/ l 6o E .75e l ,48 s 42 .758! 24 l' E 65e I l 65 E e 3e /se l i I24: .55e I g .55e I E i 5o S2 r l E e I 45] n l l .35e I 88 .35e m 24 3224C .25e 94 .25e i /22 90 24 .|5e .|5e I M 20 se E 24 ose 92 se -9e 70 Ee n 'r4 68 [L Il L A/ A rx 7 so 7o E 12 ze g A 5` E O ei l 3 9e i 5 62@se i E i |1- -40 15]- mbe t m i Qe' Y 9a l1-E EP--l .2e 96 l'E- 70 MTE[E .e e (s4 m o 1 BAEL- AT TORNEY FIG. 2 BO/ F'G" sa 96 mvENToRv Oct.20, 1959 A. LoNG 2,909,747

POTENTIOMETER Filed .July 2, 1958 2 Sheets-Sheet 2 FIG. 6

INVENTOR.

ALEXANDER LONG ATTRNEY United States Patent O POTENTIOMETER AlexanderLong, Alexandria, Va., assignor to Servonics, Inc., a corporation ofVirginia Application July 2, 1958, Serial No.` 746,273 11 Claims. (Cl.338-130) This invention relates to a precision potentiometer capable ofcontinuous rotation at relatively high speed.

Whereas the conventional Kelvin-Varley potentiometer is quite adequatefor precision purposes in the laboratory Where switching is performedmanually, it is entirely unadapted for uses involving continuousrotation, continuous balance, automatic systems, or high speedoperation.

It is accordingly among the objects of this invention to satisfy theneed for a high speed continuously rotatable precision potentiometerincorporating certain of the Kelvin-Varley principles and furthercharacterized by its: high degree of linearity, adaptability for usewith direct -or alternating current over a wide frequency range withoutphase shift; small'size; low operating torque; lack of mechanical stopsand clutches; and light weight.

A potentiometer conforming kto the present'inven- .tion comprises a pairof input terminals, similar banks of series resistors adapted to beconnected in circuit across these terminals, the resistors of each bankhaving terminals arranged in an arc, a pair of segmental variableresistors having terminals defining opposed gaps, brushes forsequentially connecting the terminals of each segmental resistor topairs of terminals of the resistor banks respectively, a wiper having aneffective span exceeding the width of each of said gaps sequentiallycontacting the segmental resistors, switching means periodicallyinterrupting the circuit between the input terminals and one of thebanks, and driving means for imparting synchronous movements to thebrushes, wiper and switching means. The driving means is preferablyrotatable continuously through an arc exceeding 360, and the brushes,wiper and switching means are likewise preferably rotatable. Theswitching means may include a pair of switches connected in parallel anddriven at dissimilar speeds. One of the switches may be driven at thesame speed as the wiper,V

and the other at the speed of the brushes. Reduction gearing is providedfor rotating the wiper and brushes at dissimilar speeds, describedherein as having a ratio of ten to one.

A more complete understanding of the invention will follow from adescription of the accompanying drawings wherein:

Fig. 1 is a circuit diagram of an arrangement embodying the invention;

Fig. 2 is a circuit diagram depicting the positions assumed by the partsof Fig. 1 after the driving shaft has advanced one-half turn;

Fig. 3 is a circuit diagram depicting the positions assumed by the partsof Fig. 1 after the driving shaft advanced nine and one-half turns;

, Fig. 4 is an exploded perspective View of the parts of a potentiometeraccording to the present invention;

Figs. 5, 6 and 7 are plan views of commutator cards employed;

Figs. 8 and 9 are perspective views of brush assemblies which cooperatewith the commutator cards;

Fig. 10 is a perspective View of one of the xed resistors; and

Fig. 1l is an elevation of an assembled potentiometer.

As will appear from Fig. 1 of the drawings, each of two resistor banks20 and 22 is made up of eleven resistors connected in series, each bankincluding ten resistors 24 each having a value of 2r and one resistor 26having a value of r. The resistor banks 20 and 22 are connected inparallel across a pair of input terminals 28 and 30, a pair of parallelswitches 32 and 34 being interposed between one input terminal 30 andthe resistor bank 22. The resistors 24 are provided with terminalslettered A to K for the bank 20, and O to Y for the bank 22. Whereaseach of the groups of terminals A to K and 0 to Y is actually arrangedin an annular fashion, they have been depicted in developed form inFigs. 1 to 3.

A Vernier potentiometer 36 cooperating with the resistor banks, iscomposed of two helically wound sections 38 and 40, each extendingthrough an arc of slightly less than 180, and a rotatable wiper 42adapted to tap the turns of these sections and of sucient width tobridge the gaps defined between the two sections. The sections 38 and 40are adjusted to a precise value of 2r each by means of parallelconnected trimmer resistors 44 and 46 respectively. The terminals 48 and50 of the section 38 of the potentiometer are connected through a pairof slip rings 52 and 54 to a pair of brushes 56 and 58 respectively,which sequentially engage the terminals A to K of the resistor bank 20.As shown in Fig. l, the brushes 56 and 5S are in contact with theterminals A and B respectively, while in Fig. 3 they have advanced toengage the terminals I and K, also respectively. In a similar manner,terminals 60 and 62 of the section 40 of the potentiometer are connectedthrough a pair of slip rings 64 and 65 to a pair of brushes 68 and 70,respectively, which wipe over the terminals O to Y of the `owing in eachbank of resistors will be the same, and

the voltage drop across the terminals A and B under the conditionsdepicted in Fig. 1 where the effective resistance is r will be the sameas across the terminals 28 and O of the bank 22 where the effectiveresistance of the uppermost resistor 26 is also r. Since the terminal Bof the bank 20 is at the same potential as the terminal O of the bank22, if the brush or wiper 42 moves counterclockwise from its positionbridging the upper gap between the sections 38 and 40 as depicted inFig. 1, it will interpolate the resistor having terminals A and B whilethe brushes 56 and 58 are moving over these terminals respectively. Byproperly synchronizing the movements of these brushes 56 and 58 withthat of the wiper 42, the brushes will reach the forward (lower inFig. 1) edges of these terminals A and B at the same time the wiper 42completes a half turn to a position in which it bridges the lower gapexisting between the terminals 50 and 62 of the sections 38 and 40respectively, as shown in Fig. 2. While these movements have beenoccurring, the brushes 70 and 68, synchronized for movement at the samerate as the brushes S6 and 58, have traveled from their positionscontacting the terminals X and Y in Fig. l to the positions in contactwith the terminals O and P as shown in Fig. 2.

Assuming the input Voltage applied across the terminals ma h 28 and30'to have the value e, the potential difference between the terminalsV30 and A will be .95e and that between the terminals 30 and O willlikewise be .95e. Hence, the `same potentials, will .exist atV theterminalsSt) and/62 'of the two sections bridged bythe wiper 42 `in Fig.2 so that whenthe wiper moves farther in itsl counte'rclockwise'rotationto break its Contact with thesection SS'therewill be nofow of currentvnor production ofA transients,

Then as the wiper 42 proceeds to scan the turns of the section 40 itwill interpolate Values between .95e and .90e until -it once againbridges the upper gap between the terminals 48and 60 of the sections 38and 40. By this time the brush 56 will have moved into contact with theterminal B whose potential is now .90E corresponding to that at theterminals P and 60. In this fashion, the output potential between theoutput terminals 72 and 74 will be derived alternately from the resistorbanks 20 and 22 to produce linear values in a continuous fashion. Therelative positions of the brushes after movement of the wiper 42 throughnine and onehalf turns, as comi pared with Fig. l, has been depicted inFig. 3, where the wiper 42 is about to interpolate between the values.05e

and Zero, during which the brushes 56, 58, 68 and 70.

will return to the positions which they previously assumed in Fig. l. Itwill be clear, of course, that the direction of rotation can becontinuous or may be changed if desired.

The wiper 42 is driven direct by a shaft 76, depicted by a broken linein Fig. l. likewise driven by the shaft 76, imparts one revolution tothe brushes 56, 58, 68 and 70 for each ten of the wiper 42 throughsuitable shafting depicted by broken lines 80 and 82 in Fig. l.

Also driven at one-tenth the speed of the wiper 42 through the l:lreduction gearing 78 and shafting represented in Fig. l by broken lines84 and 86, are the rotary brushes 88 and 90 of the switches 32 and 34respectively. The switch 32 includes a 360 inner slip ring 92` and anouter segmental slip ring 94 extending through an arc of approximately1791/2 and its. brush 88 synchronized with respect to the wiper 42 so asto open the circuit between the slip rings 92 and 94 during slightlymore than one-half of a revolution of the wiper 42. The switch 34includes a 360 outer slip ring 96 and a segmental inner slip ring 98extending through an arc of approximately 342, and a brush 90 driventhrough thew reduction gearing 78 in synchronism with the brush 88 tocontrol the circuit between its slip rings 96 and 98. The timing is suchthat the circuit between the slip rings 96 and 98 is interrupted onceduring each ten turns of the wiper 42 when the brush 68 is in contactwith its terminal Y and the brush 56 is just about to contact itsterminal A. Were the switch 34 not open at this time, with the wiper 42bridging the gap between the terminals 48 and 60, a short circuit acrossthe input terminals 28 and 30 would occur, from the terminal. 28,terminal A, brush 56, terminal 48, wiper 42, terminal 60 brush 68 andterminal Y to the terminal 30. The switch 32, driven at the same rate asthe wiper 42, is connected in parallel with the switch 34. as kfurtherassurance against such short cir.

Suitable reduction gearing 78,.

O to Y inclusive.

cuiting. Except for the transition period during which the circuit is tobe interrupted, the switch 34 remains closed so that the switch 32 isrendered ineffective to open the circuit. However, should errors bepresent that would of rotation, the circuit would be interrupted by theswitch 32 during the proper period.

has been illustrated in Figs. 4 to 11. An insulating disk 65 bemultiplied by the switch 34 because of its reduced rate 100 shown inFig. 6 carries the slip rings52, 54 and 981.1

and the terminals A to K inclusive. As clearly shown,

the terminal A is partiallyicoextensive arcuately with the terminal Kdisposed radially outwardly therefrom,for

cooperationwith their (brushes 56 and 58 shown in Fig. 8

proximately 36. As shown in Fig. 4, the terminals A to K are connectedto their tixed resistors by means of leads 102 extending through thedisk 100.

Similarly, an insulating disk 104 depicted in Fig. 7, carries the sliprings 64,. 66.and, 98 `and the terminals In this case the terminals Oand Y are partially coextensive and radially displaced, as are theterminals A and K of the disk 100, for cooperation with their similarlydisplaced brushesY 68 and 70.

As will be noted from Figs. 6 and 7, the terminals F and T lare dividedto form radially displaced segments F and F1 on the one hand, and T andT1 on the other, bridged by jumpers 106. Should it ybe desirable tooperate the potentiometer at one-half input potential, the jumpers 106can be removed and `suitable connection can be made from these segmentsto center tap terminals 108 and 110 shown in Fig. 4.

As clearly shown in Fig. 8, the .brushes 68 Vand 70 are supported Aby aninsulating block 112 having a shaft 114 for rotary contact withtheirslip rings 64 and 66 respectively, and the terminals O to Y of theresistor bank 22. Similarly, the block 112 supports the brushes 56 and58 for rotary contact vwith their slip rings 52 and 54 respectively, andthe terminals A to K of the resistor bank 20. As will-'be evident fromFig. 4, the block 112 is interposedV between the disks 100 and 104 forswitching engagement with-the terminals and slip rings of both. Theblock .112-also-carries the brushes for cooperation with the Yslip rings96 and 98 supported by the disks 104 andf respectively.

Another insulating disk 116 depicted in Fig. 5 carries a slip ringv118-connected to the output terminal 72, whose brush 120 establishes aconnection to the wiper 42. This disk also carries the sliptrings 92 and94. The brush carrier'122 shown in Fig. 9 supports the wiper 42 andbrushes 88 and 120 for cooperation with the slip rings carried bythedisk 116 and the two sections 38 and 40 of the Vernier potentiometer36.-

In its assembled form as depicted in Fig. 11, the device is housed'in acylindrical casing 126 vto which a terminal block 128V is suitablyfastened for supporting pins defining `the terminals 28, 30, 72, 74, 108and 110. The resistors 24 are wound on rectangular cores 130 in bilarfashion, as shown in Fig. l0, and arranged radially as shown in Fig. 4,their leads 102 extending to their respectiveV terminals A to K of theresistor bank 20 and on a shaft 138 carried by a plate k139 to which thedisk 116 `is secured.v The drive shaft V76 carrying the block or v.brush'carrier 122 terminates in a small gear 140 which projects through acentral opening 142 of the vdisk 116 for .engagement-with'the teeth ofthe larger gear 136. Threaded--openings 144 formed in the plate `139receive the ends of rods 146 which project through openings formed. inthe disks 100 and 104 to vassure their proper relative positions afterassembly. A cover member 148 containing-an opening 150 through which theshaft 76 projects, houses the Vernier potentiometer sections 38 and 40and is suitably secured to the casing 126.

Whereasthe invention has been described with respect toV asingleembodiment for purposesof illustration, it is not intended to be limitedthereto beyond the-scope ofthe appended claims.

I claim :v

1. A potentiometer comprisingqa pair of..inputv terminals, similar banksof series resistors, each bank being.

connected in circuit across said input terminals, said resistors of eachbank having terminalsarranged in an arc, u

a pair of segmental variable resistors having terminals defining opposedgaps, brushes for sequentially connect ing the terminals of each of saidsegmental resistors to pairs of terminals of said resistor banksrespectively, a wiper having an effective span exceeding each of saidgaps sequentially contacting said segmental resistors, switching meansperiodically interrupting the circuit between said input terminals andone of said banks, and driving means for imparting synchronous movementsto said brushes, wiper and switching means.

2. A potentiometer as set forth in claim l wherein said driving means isrotatable.

3. A potentiometer as set forth in claim 1 wherein said driving meansincludes a shaft rotatable through an arc exceeding 360.

4. A potentiometer as set forth in claim l wherein said switching meansis rotatable.

5. A potentiometer as set forth in claim 1 wherein said switching meansincludes a pair of switches connected in parallel and driven atdissimilar speeds.

6. A potentiometer as set forth in claim l wherein said driving meansincludes reduction gearing for rotating said brushes and wiper atdifferent speeds.

7. A potentiometer as set forth in claim 1 wherein said driving meansincludes reduction gearing for rotating said wiper and switching meansat different speeds.

8. A potentiometer comprising a pair of input terminals, a pair of banksof resistors adapted to be connected in parallel with said inputterminals, each bank containing a like number of resistors of equalvalue connected in series, taps from the resistors of each bank beingannualarly disposed, a pair of Vernier resistor seg ments, said segmentsbeing annularly disposed with gaps between adjacent segments, eachsegment having a resistance value equal to that of each said resistor ofsaid banks, each segment having brushes adapted to contact adjacentpairs of taps of one of said banks, a wiper having an effective widthgreater than each of said gaps adapted to scan each of said segmentssequentially, a rotary switch interposed in circuit between said inputterminals and one of said banks, and driving means connected with saidbrushes, wiper and switch for effecting synchronous movement thereof.

9. A potentiometer as set forth in claim 8 wherein said brushes andwiper are so synchronized that adjacent terminals defining each gapbetween said segments are at equal potential each time said wiperassumes a gap bridging position.

l0. A potentiometer as set forth in claim 8 wherein said annularlydisposed taps are carried on proximate surfaces of spaced supports, andsaid brushes for both banks are interposed between said supports.

1l. A potentiometer as set forth in claim 8 wherein said brushes, wiperand switch are continuously rotatable.

References Cited in the ile of this patent UNITED STATES PATENTS2,498,967 Schaefer Feb. 28, 1950 2,501,813 Franklin Mar. 28, 19502,572,545 Walker Oct. 23, 1951

